Patent Document 1, Patent Document 2, and Patent Document 3 respectively discuss a shock absorber for a vehicle, assembled into bumper beams respectively disposed on a front face or a rear face of a vehicle body of the vehicle and deformed by a shock applied when the vehicle collides with an object having a low rigidity to cushion a shock exerted on the object, so adapted that a concavely curved supporting wall is formed from a second wall to a first wall of a hollow double-wall structure and welded to the first wall, a shock absorber for a vehicle so adapted that a pair of recessed ribs is formed from a first wall and a second wall of a hollow double-wall structure and is welded within a hollow portion, and a blow molded energy absorber for a front end of a vehicle having an integral structure, serving as a hollow double-wall structure, including a forward projection and a backward portion attached to the vehicle.
Patent Document 1: Japanese Patent Application Laid-Open No. 2004-114864
Patent Document 2: Japanese Patent Application Laid-Open No. 2006-151250
Patent Document 3: Japanese Patent Application Laid-Open No. 2006-519730